System for Offshore Carbon Dioxide Capture

Abstract

A capture system for offshore carbon dioxide capture and a method for offshore carbon dioxide capture are described. A capture system for offshore carbon dioxide capture, the system comprising: a pressurised flue gas source configured to provide a pressurised flue gas 101; a solvent source configured to provide a liquid solvent; and a two-phase atomising nozzle in fluid communication with the pressurised flue gas source and the solvent source; wherein the two-phase atomising nozzle is configured for two-phase flow of a mixture of the pressurised flue gas and the liquid solvent in order to generate an atomised solvent spray of the liquid solvent.

Claims

1. A capture system for offshore carbon dioxide capture, the system comprising: a pressurised flue gas source configured to provide a pressurised flue gas; a solvent source configured to provide a liquid solvent; and a two-phase atomising nozzle in fluid communication with the pressurised flue gas source and the solvent source; wherein the two-phase atomising nozzle is configured for two-phase flow of a mixture of the pressurised flue gas and the liquid solvent in order to generate an atomised solvent spray of the liquid solvent.

2. The capture system as claimed in claim 1, wherein the pressurised flue gas is configured to drive the solvent through the two-phase atomising nozzle to generate the atomised solvent spray.

3. The capture system as claimed in claim 1, wherein the atomised solvent spray, upon generation, comprises solvent droplets having a droplet diameter of 150 μm or less.

4. The capture system as claimed in claim 1, wherein the pressurised flue gas source is a gas turbine engine.

5. The capture system as claimed in claim 4, wherein the pressurised flue gas is taken from an exhaust gas of the gas turbine engine, and wherein the remaining exhaust gas is passed through a waste heat recovery unit before being passed through the atomised solvent spray.

6. The capture system as claimed in claim 5, wherein heat recovered from the waste heat recovery unit is configured to produce hot pressurised water and/or hot pressurised oil for solvent regeneration.

7. The capture system as claimed in claim 1, wherein a solvent regeneration unit is configured to separate solvent from any solute present in the solvent, preferably wherein the solute is carbon dioxide.

8. The capture system as claimed claim 7, wherein the solvent regeneration unit is the solvent source.

9. The capture system as claimed in claim 1, further comprising a direct contact cooler downstream of the atomised solvent spray, wherein the direct contact cooler is configured to condense the atomised solvent spray.

10. The capture system as claimed in claim 1, further comprising one or more demisters configured to condense the atomised solvent spray.

11. The capture system as claimed in claim 1, wherein the atomised solvent spray is configured to capture carbon dioxide present in the pressurised flue gas.

12. An offshore vessel comprising the system as claimed in claim 1.

13. The offshore vessel as claimed in claim 12, wherein the offshore vessel is configured to use seawater to cool the system.

14. A method for offshore carbon dioxide capture, the method comprising: providing pressurised flue gas to a two-phase atomising nozzle; providing liquid solvent to the two-phase atomising nozzle; and generating an atomised solvent spray using the two-phase atomising nozzle; wherein the two-phase atomising nozzle is configured for two-phase flow of a mixture of the pressurised flue gas and the liquid solvent in order to generate the atomised solvent spray of the liquid solvent.

15. The method as claimed in claim 14, further comprising: driving the liquid solvent through the two-phase atomising nozzle using the pressurised flue gas.

16. The method as claimed in claim 14, comprising: capturing carbon dioxide present in the pressurised flue gas using the atomised solvent spray.

17. The method as claimed in claim 14, comprising: taking a flow of pressurised flue gas from an exhaust gas of a gas turbine engine; and passing the flow of exhaust gas through a waste heat recovery unit before passing the flow of exhaust gas through the atomised solvent spray.

18. The method as claimed in claim 14, comprising: separating solvent from any solute present in the solvent using a solvent regeneration unit, preferably wherein the solute is carbon dioxide.

19. The method for offshore carbon dioxide capture, wherein the method is performed by the capture system of claim 1 or the offshore vessel as claimed in claim 12.

Description

[0105] Certain example embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

[0106] FIG. 1A shows a vessel with a carbon capture system installed on board;

[0107] FIG. 1B shows a proportionally representative view of a carbon capture system and a gas turbine engine of the vessel of FIG. 1A;

[0108] FIG. 2 illustrates a schematic diagram of carbon capture system;

[0109] FIG. 3A shows a simulated graph of carbon dioxide concentration in a flue gas in a carbon capture system as a function of time; and

[0110] FIG. 3B shows a simulated graph of a carbon dioxide concentration in a liquid solvent in a carbon capture system as a function of time.

[0111] FIG. 1A shows a vessel 1. Whilst the vessel 1 as illustrated resembles a ship, it is to be appreciated that the vessel 1 may be any marine-based platform, such as a floating oil rig, a static oil rig, or a ship and/or boat of any size. Installed on board the vessel 1 is a carbon dioxide capture system 100 (herein referred to as capture system 100) and a gas turbine engine 200. The capture system 100 and the gas turbine engine 200 shown installed on the vessel 1 are proportionally representative of the footprint they may occupy on the vessel 1. The gas turbine engine 200 may comprise one or more gas turbines used, for example, for providing a thrust via a propeller to propel the vessel 1 as required, or for the generation of electrical power to one or more components of the floating vessel 1.

[0112] FIG. 1B is a more detailed representation of the capture system 100 and the gas turbine engine 200 installed on the vessel 1 of FIG. 1, as encircled. A person 3 is shown next to the capture system 100. The person 3 is proportionally representative of the size of the capture system 100. The capture system 100 comprises a substantially narrow, vertical profile. Accordingly, the width of the base of the capture system may be 12 m and the height hi of the capture system may be 20 m. Whilst not shown in FIG. 1A, the capture system 100 is in flow communication with an exhaust of the gas turbine engine.

[0113] The capture system 100 as illustrated in FIG. 1A comprises three general sections. At the base of the capture system 100 there is a waste heat recovery unit (WHRU) 120. On top of the WHRU 120 is an absorber 110. Placed on top of the absorber 110 is a direct contact cooler 130. The direct contact cooler 130 may comprise a water wash. Whilst not shown in FIG. 1B, the capture system 100 may also comprise a solvent regeneration unit 140. The absorber 110 may have a diameter of 7 m, and a height of 11 m. By stacking the components of the capture system 100 on top of one another in a generally vertical fashion, the footprint of the capture system 100 on board the vessel 1 may be reduced.

[0114] FIG. 2 shows a schematic diagram of the capture system 100 in flow communication with the gas turbine engine 200. The capture system 100 removes carbon dioxide from a flue gas, such as a pressured flue gas 101, by treating it with a liquid solvent 102. To maximise the efficiency of the capture process, a two-phase atomising nozzle 103 facilitates a mixing of a pressurised flue gas 101 and a liquid solvent 102 by generating an atomised solvent spray 104, as described herein.

[0115] The pressurised flue gas 101 is provided to a two-phase atomising nozzle 103. The pressurised flue gas 101 is in a gaseous phase. A liquid solvent 102 is also provided to the two-phase atomising nozzle 103. The liquid solvent 102 is a lean solvent; that is, the liquid solvent 102 provided to the two-phase atomising nozzle 103 is not loaded with solute. The two-phase atomising nozzle 103 generates an atomised solvent spray 104. The atomised solvent spray 104 comprises a mixture of the pressurised flue gas 101 and the liquid solvent 103.

[0116] The pressurised flue gas 101 is of sufficient pressure such that the liquid solvent 102 is driven through the two-phase atomising nozzle 103 to produce the atomised solvent spray 104. Sufficient pressure herein is defined as a pressure greater than the pressure of treated gas 131 exhausted from the capture system 100 via the direct contact cooler 130, such that the liquid solvent 102 is motivated through the two-phase atomising nozzle 103 to produce the atomised solvent spray 104. Accordingly, the pressurised flue gas may be of a pressure greater than that of the treated gas 131 by 6 kPa or less, 5 kPa or less, or 3 kPa or less, as required.

[0117] The pressurised flue gas 101, as well as being of sufficient pressure to drive the liquid solvent 102 through the two-phase atomising nozzle 103, is also of sufficient pressure to generate droplets of liquid solvent 102 in the atomised solvent spray 104 which have a droplet diameter of less than 150 μm, less than 100 μm, or with diameters from 25 μm to 150 μm, or with diameters from 50 μm to 100 μm, as it drives the liquid solvent 102 through the two-phase atomising nozzle 103. The droplet diameter may be defined according to the Sauter mean particle diameter.

[0118] The capture of carbon dioxide from the pressurised flue gas 101 is enhanced by the two-phase atomising nozzle 103 as the produced atomised solvent spray comprises a number of solvent droplets which increase the effective surface area of the liquid solvent 102. As such, and as will be readily understood by the skilled person, a large contact surface is provided between the liquid phase, i.e. the liquid solvent 102, and the gaseous phase, i.e. the pressurised flue gas 101, such that capture and/or absorption of carbon dioxide from the gaseous phase is increased. A co-current flow between the pressurised flue gas 101 and the atomised solvent spray 104 may also increase the time in which the pressurised flue gas 101 and the atomised solvent spray 104 are in contact, thus increasing the capture and/or absorption of carbon dioxide from the gaseous phase.

[0119] Whilst two two-phase atomising nozzles 103 are shown in FIG. 2, the capture system may comprise one or more two-phase atomising nozzles 103 as necessary. For example, the two-phase atomising nozzle 103 may be a battery of 220 or more two-phase atomising nozzles 102. The two-phase atomising nozzles 103 are appreciably lighter in weight than conventionally used solid packed solvent. Accordingly, the use of two-phase atomising nozzles 103 within the capture system 100 may reduce the weight of the capture system 100.

[0120] The two-phase atomising nozzle 103 is housed in a large vat or tank. This may be referred to as the absorber 110, and is where the treatment of the pressurised flue gas 101 by the atomised solvent spray 104 occurs. So that the pressurised flue gas 101 treated by the capture system 100 (herein treated gas 131) may be exhausted from the system, whilst liquid solvent is recycled and/or reused by the capture system 100, one or more demisters 105 may be placed in the absorber 110 downstream of the atomised solvent spray 104. The demisters 105 may be mesh-pad demister 105a and a chevron vane demister 105b. Whilst a mesh-pad demister 105a and a chevron vane demister 105b are shown herein, any combination or number of demisters 105 may be implemented as required. For example, the demisters could be a Brownian diffusion demister, or a device with a filter fabric of smaller pores to further separate droplets smaller than those of chevron vane demisters, mesh-pad demisters or Brownian diffusion demisters.

[0121] The demisters 105 condense larger droplets of the atomised solvent spray 104, whilst smaller droplets may pass through given their size. The treated gas 131 passes through the demisters 105. The atomised solvent spray 104 which is condensed pools at the base of the absorber 110, upstream of the two-phase atomising nozzle 103. The condensed atomised solvent spray 104 forms a sump volume 106. The sump volume 106 comprises a mixture of condensed liquid solvent 102 that has captured carbon dioxide from the pressurised flue gas 101. As such it may be regarded as ‘loaded’, and is thus rich solvent. The sump volume 106 may also comprise liquid water.

[0122] The smaller droplets of liquid solvent 102 which are not condensed in the demisters 105 of the absorber 110 are carried by the pressurised flue gas 101 into a direct contact cooler 130. The direct contact cooler 130 is housed in a columnar tank and/or vat, stacked on top of the absorber 110. The direct contact cooler 130 is downstream of the absorber, and is separated from the absorber by the demisters 105. The direct contact cooler 130 comprises an outlet 136 by which the treated gas 131 is exhausted from the capture system 100.

[0123] Advantageously, the capture system 100 may only require a single direct contact cooler 130, located downstream of the two-phase atomising nozzle 103. As the two-phase atomising nozzle 103 negates the need for the conventional packed solvent used in the prior art, a direct contact cooler 130 is not required to cool the pressurised flue gas 101 before it meets a packed solid solvent. Accordingly, the weight and footprint of the capture system 100 may be reduced. Whilst only a single direct contact cooler 130 may be required and is shown in the capture system 100 of FIG. 2, more than one direct contact cooler 130 may be implemented in the capture system 100.

[0124] One or more water spray nozzles 133 are located in the direct contact cooler 130, which receive liquid water 132 and generate a water wash 134 comprising the liquid water 132. The water wash 134 is co-current with the treated gas 131 and the smaller droplets of liquid solvent 102 which pass through the direct contact cooler 130. Accordingly, the smaller droplets of liquid solvent 102 of the atomised solvent spray 104 which pass into the direct contact cooler 130 are passed through the co-current water wash 134. The use of a co-current water wash 134 may reduce the pressure drop across the capture system 100 such that the pressurised flue gas source 101 may be of suitable pressure to be the motive gas for the two-phase atomising nozzle 103.

[0125] The liquid water 132 in the co-current water wash 134 causes the smaller droplets of liquid solvent 102 to form larger droplets. The larger droplets of liquid solvent 102 then condense, as does the water 132, in a series of demisters 135 located at the outlet 136 of the direct contact cooler 130. As with the absorber 110, the demisters 135 may be a mesh pad demister 135a and a chevron vane demister 135b. Any number and type of demisters 135 may be implemented as required. The condensed liquid solvent 102, which typically rich (i.e. ‘loaded’) solvent, and condensed liquid water 132, is collected by a vane collector 137 and passes into the absorber 110, where it pools at the base in the sump volume 106.

[0126] Some of the liquid water 132 present in the co-current water wash 134 may be collected at the vane collector 137 and pumped, via a pump 138, back to the water spray nozzles 133. Before being passed back to the water spray nozzles 133, the liquid water 132 may be passed through a heat exchanger 138. The heat exchanger 138 cools the liquid water 132 such that the water wash 134 is cool enough to sufficiently condense the liquid solvent 102. The heat exchanger 139 may use seawater to cool the liquid water 132.

[0127] The sump volume 106, comprising rich liquid solvent 102 and any liquid water 132 from the direct contact cooler 130 or otherwise, is passed from the absorber 110 to a solvent regeneration unit 140 via a sump pump 141. The liquid solvent 102 and liquid water 132 may pass through a solvent heat exchanger 143, where rich liquid solvent 102 exchanges heat with lean liquid solvent 102 generated by the solvent regeneration unit 140. The rich liquid solvent 102 is heated by the lean liquid solvent 102 in the solvent heat exchanger 143, such that less energy is required by the solvent regeneration unit 140 in regenerating lean liquid solvent 102 from the rich liquid solvent 102.

[0128] The solvent regeneration unit 140 recycles rich liquid solvent 102, loaded with captured carbon dioxide from the pressurised flue gas 101, by stripping the liquid solvent 102 of said captured carbon dioxide. The solvent regeneration process may be performed by any known conventional process for releasing the captured carbon dioxide from the liquid solvent. For example, a number of reboilers and structured packing could be configured to selectively desorb carbon dioxide. Generally, the solvent regeneration process may adjust the equilibrium of the capture process such that carbon dioxide is released in a gaseous form. It may then be stored used conventional carbon dioxide storage methods. The stripped, i.e. lean, liquid solvent 102 is then returned to the two-phase atomising nozzle 103. In this respect, the solvent regeneration unit 140 may therefore be regarded as a liquid solvent source. The liquid solvent 102 provided from the solvent regeneration unit 140, having passed through the solvent heat exchanger 143 is passed through an additional heat exchanger 144. The heat exchanger 144 cools the liquid solvent 102 using seawater. Cooling the liquid solvent 102 before passing it to the two-phase atomising nozzle 103 may help prevent the evaporation of the liquid solvent 102 as it is atomised into the liquid droplets forming the atomised solvent spray 104.

[0129] The use of seawater cooling at various instances of the capture system 100 may reduce the energy demands of the capture system 100. As the capture system 100 is installed on a vessel 1, there is an abundance of seawater available which may cool the various components of the capture system 100 as required. The seawater, once heated, need not be cooled by additional cooling devices. Instead, a constant flow of seawater from the surrounding environment may instead be used. Accordingly, the use of seawater may increase the energy efficiency of the capture system 100.

[0130] Whilst seawater is discussed in relation to the present embodiment, it will be readily understood that any large body of water could provide an abundance of cooling water for used in the capture system 100. As such the capture system 100 could be utilised onshore nearby a river, lake or other appropriate water source.

[0131] The solvent regeneration unit 140 also separates liquid water 132 from the liquid solvent 102, and returns the liquid water 102 to the direct contact cooler 130. Heat required for the solvent regeneration process may also be provided by pressurised water and/or oil 122. The heat from the pressurised water and/oil 122 is transferred to the solvent regeneration unit 140 using a heat exchanger 142.

[0132] The capture system 100 also comprises the WHRU 120. The WHRU 120 is located beneath the absorber 110. Exhaust gas 201 is taken, split and/or divided from the pressurised flue gas 101 and passed through the WHRU 120. The exhaust gas 201 passed through the WHRU 120 may be an excess of pressurised flue gas 101 which may not all be passed through the two-phase atomiser nozzle 103 without undesirable flow effects, such as turbulence, or pressure build-ups, occurring. The WHRU 120 comprises a number of heat exchangers 121. The WHRU 120 may comprise any number of heat exchangers 121 as required. The heat exchangers 121 transfer heat from the exhaust gas 201 to pressurised water and/or oil 122. The pressurised water and/or oil 122 then transfers the heat to the solvent regeneration unit 140, for use in the solvent generation process. Accordingly, heat which may otherwise be regarded as a waste product is used in a different, advantageous element of the capture system 100.

[0133] The exhaust gas 201 which has had waste heat extracted from it via the one or more heat exchangers 120 is then passed through the absorber 110. The exhaust gas 201 is passed through the atomised solvent spray 104, along with the pressurised flue gas 101 which is passed directly through the atomised solvent spray 104 via the two-phase atomising nozzle 103. As such the exhaust gas 201 may also be treated and have carbon dioxide present in it captured by the liquid solvent 102. Accordingly, the treated gas 131 comprises the pressurised flue gas 101 passed through the atomised solvent spray 104 via the two-phase atomising nozzle and the exhaust gas 201 passed through the atomised solvent spray 104 via the WHRU 120.

[0134] As will be appreciated by the skilled person, whilst only the pressurised flue gas 101 passed to the two-phase atomising nozzle 103 drives the liquid solvent 102 through the two-phase atomising nozzle 103 to generate the atomised solvent spray 104, both the pressurised flue gas 101 and the exhaust gas 201 act as the flue gas for the capture system downstream of the absorber 110, given that both may be regarded as the treated gas 131 once they have been passed through the atomised solvent spray 104. Whilst referred to as a flue gas, the pressurised flue gas 101 and/or the exhaust gas may also be regarded as a motive gas.

[0135] The pressurised flue gas 101 and the exhaust gas 201 shown in FIG. 2 are provided to the absorber 110 and the WHRU 120 respectively by the gas turbine engine 200. In this respect, the gas turbine engine 200 may be regarded as a pressurised flue gas source. The gas turbine engine 200 comprises a heat exchanger 202, the heat exchanger 202 configured to cool the pressurised flue gas 101 before it is provided to the two-phase atomising nozzle 103.

[0136] As illustrated in FIG. 2, the gas turbine engine 200 comprises an air inlet 203 such as a fan, a low pressure compressor 204, a high pressure compressor 205, a combustor 206, a low pressure turbine 207, a high pressure turbine 208, and an air outlet 209. The structure of the gas turbine engine 200 need not be limited to the structure shown in FIG. 2, but may be any gas turbine engine 200 which is capable of producing a sufficiently pressurised flue gas source 101. The pressure of the pressurised flue gas source 101 may for example be provided by a back-pressure of the exhaust product of the gas turbine engine 200. The compressors 204, 205 present in the gas turbine engine 200 may provide the pressure required for the pressurised flue gas source 101. Whilst described herein as a pressurised flue gas source 101, separate to an exhaust gas 201 provided to the WHRU 120, it is to be appreciated that the pressurised flue gas 101 may also be the exhaust product of the gas turbine engine 200.

[0137] The pressurised flue gas source 101 need not necessarily be a gas turbine engine 200. The pressurised flue gas source 101 could be any combustion engine or other engine producing compounds such as carbon dioxide. Alternatively, a compressor, fan, blower or pump could be utilised to treat ambient air (i.e. at standard temperature and standard pressure) by pressurising and/or warming it, before passing it to the two-phase atomising nozzle 103.

[0138] FIGS. 3A and 3B illustrate different simulated variables for a simulation of the capture system 100. FIG. 3A shows how the carbon dioxide concentration in the pressurised flue gas 101 reduces as it is treated by the atomised solvent spray 104 and becomes treated gas 131. FIG. 3B shows how the carbon dioxide content of the liquid solvent 102 increases as the pressurised flue gas 101 and the exhaust gas 201 are passed through the atomised solvent spray. Table 1 shows a list of pre-determined input variables used to simulate the capture system 100.

TABLE-US-00001 TABLE 1 Input variables for a simulation of the capture system 100. Solvent 30% wt MEA Liquid/gas ratio 3 kg/kg Droplet diameter 50 μm Temperature 45° C. Residence time 3 s Initial loading 0.22 kmol CO.sub.2/kmol MEA Initial CO.sub.2 concentration 5.7%

[0139] Whilst the simulation was performed for a liquid solvent 102 comprising 30% wt monoethanolamine (MEA), piperazine or mixtures thereof may also be used as the liquid solvent 102. Similarly, the mixture may be 20% wt MEA, 60% wt MEA, or any other weight percentage of MEA which achieves a similar capture rate. The simulation also assumes that there is a co-current gas-liquid flow of droplets in the atomised solvent spray 104 and of the pressurised flue gas 101.

[0140] As shown in FIGS. 3A and 3B, as the gas interacts with the droplet over the course of the 3 second residence time carbon dioxide is captured from the gas and loads the solvent droplet. The efficiency of the capture system 100, for this base simulation, is around 75% carbon dioxide capture.

[0141] The capture system 100 may hence be capable of efficiently capturing carbon dioxide from a flue gas. The environmental advantages of removing carbon dioxide are well understood and as such the capture system 100 may be regarded as capable of advantageously reducing the environmental impact of a gas rich in carbon dioxide. The gas may be an exhaust product of a gas turbine engine 200, and thus the capture system 100 may reduce the environmentally harmful impact of the combustion of gas in a gas turbine engine 200.

[0142] Further, by using the exhaust products of gas turbine engine 200, e.g. the pressurised flue gas 101, to drive the liquid solvent 102 used for carbon capture through the two-phase atomising nozzle 103 in the capture system 100, the energy requirements of the capture system 100 may be reduced. Additionally or alternatively, the use of the pressurised flue gas 101 from the exhaust product of a gas turbine engine 200 may avoid the need for additional pumps and/or compressors to adequately pressurise the pressurised flue gas 101.

[0143] Further, by avoiding the need to use a conventional scrubber column, the overall weight and footprint of the capture system 100 may also be reduced.